It has heretofore been recognized in design and operation of hydraulic and lubrication systems that control of contaminant concentration level in the circulating fluid plays an important role in system reliability. Solid particulate contaminants, such as sand, dirt and metal particles, may enter the system at the time of manufacture or upon breach of system integrity, or may result from abrasion and wear of system components. Air bubbles and water droplets may become entrained in the fluid for any number of reasons, and can cause damage and corrosion of system components. Proper selection and placement of contamination control devices can eliminate the root cause of up to 80% of system failures. In addition, proper identification of target cleanliness levels, coupled with proper selection and placement of suitable filters or other contamination control devices, allows the cost of the filters and devices to be recovered quickly by the savings of improved performance, increased component life, increased oil life, increased system up-time and reduced repairs.
In systemic contamination control, the goal is to maintain fluid cleanliness at or below the point at which contamination can be become a factor in the failure of any component in the system during the desired useful life of that system. The first step in achieving this goal is identifying and setting a target cleanliness level at the system design stage that takes into account the specific needs and components of the system. These target contamination levels are determined by component design and system operating characteristics. For example, target cleanliness level would typically be greater (lower number), and therefore allowable contamination concentration level would typically be less, for systems operating at high fluid pressure than for systems operating at low pressure. The next step is to select and position filters and other contamination control devices so that the target cleanliness level can be maintained in a cost-effective manner. The third step is to confirm that the desired target cleanliness level is being maintained. For a detailed discussion of systemic contamination control, see the "Vickers Guide to Systemic Contamination Control." Vickers, Incorporated, December 1992. The present invention is directed in particular to the third or fluid-monitoring step in the systemic approach to fluid contamination control.
Fluid cleanliness level is typically monitored by obtaining a fluid sample from the system during operation, and transmitting the sample to a laboratory that analyzes and reports cleanliness level in the form of cleanliness data in an established standard data format--e.g., ISO Standard 4406. If the target cleanliness level is being met, standard filter maintenance and periodic fluid testing are continued. If the target cleanliness level is not being maintained, a change in maintenance practices and perhaps addition or relocation of the filters, may be warranted. This conventional technique for monitoring contamination level requires several hours or days to obtain the laboratory test results, and therefore leaves much to be desired in terms of providing an accurate indication of contamination level in real time so that corrective action can be initiated before the problem becomes more serious.
It is therefore a general object of the present invention to provide a system and method for proactive maintenance of fluid cleanliness in hydraulic, lubrication and other fluid systems in which one or more sensors are placed in the fluid flow path for monitoring fluid cleanliness and providing a continuous indication of fluid cleanliness level in real time. Another and more specific object of the present invention is to provide a method and apparatus for monitoring fluid contamination level that embody no consumable parts, that possess enhanced flexibility in terms of placement in the system, that do not substantially restrict fluid flow, that are responsive to all three of the primary types of contaminants (solid particles, water droplets and air bubbles), that provide continuous and unattended monitoring in real time, that are readily programmable in the field for detecting differing target cleanliness levels, that have a sensitivity of plus or minus one ISO code, and/or that warn a user of changes in contaminant concentration level before the system pump and other fluid components are adversely affected. Another and more specific object of the present invention is to provide a fluid contamination level monitoring apparatus of the described character that is economical to manufacture, and that may be readily installed in either new or existing industrial or mobile fluid systems.